The present invention relates generally to a torsional vibration damping device used in, for instance, a torque converter having a lock-up mechanism. The invention further relates to a damping device disposed between an input member and an output member of tile torque converter for damping vibration transmitted to the output member from the input member upon engagement of tile lock-up mechanism.
A typical torque converter generally includes an annular housing (an input member), an impeller attached to the housing, and a turbine and a stator disposed within tile housing. When the torque converter is used in an automotive application, the annular housing is coupled to the drive shaft of the automobile engine for rotation therewith. The turbine is usually connected to an output member or hub which couples to the input shaft of an automatic transmission for transmitting torque thereto. As the drive shaft of the engine rotates, rotation of the torque converter housing causes the impeller to urge fluid into the blades of tile turbine. In response to the movement of the fluid, the turbine rotates and transmits torque to tile automatic transmission.
Some torque converters are provided with a lock-up device disposed between the turbine and a front cover. When the lock-up device is engaged, torque is directly transmitted through the lock-up device from the front cover to tile output member. One such lock-up device includes an elastic member such as a torsion spring disposed between the output member and the lock-up device that absorbs some of the shock produced when the lock-up device engages. However, the conventional torsion spring arrangement used in lock-up devices provides only a low level of rigidity absorbing only slight vibrations transmitted at low speed levels and cannot absorb low frequency vibration experienced at higher speed levels.
In order to solve the above described problem, the applicant of the present invention has considered a lock-up device in which a viscous damping mechanism is provided in parallel with an elastic or spring type damping mechanism. The viscous damping device includes a circumferentially extending case, the case defining a fluid chamber and a slider disposed so as to be circumferentially movable in the chamber. Fluid (hydraulic fluid in the torque converter) flows through a clearance between the case and the slider when the case and the slider are relatively rotated, to produce a desired damping effect by resistance in the clearance.
In this lock-up device, slight vibration in a low speed area is absorbed by the elastic connecting mechanism having a torsion spring low in rigidity, and low-frequency vibration in a high speed area is absorbed by the viscous damping mechanism for producing large hysteresis torque in the high speed area.
However, In the viscous damping device, if excess hydraulic fluid pressure created In the fluid chamber, clearance between the slider and the case can increase. If this clearance is increased, the amount of hydraulic fluid leaking out of the fluid chamber is increased, thereby to make it Impossible to obtain desired damping response.